Helping people whittle down their waistlines has fattened the fortunes of fitness guru Kayla Itsines, propelling her into the ranks of Australia's richest young business people.

Ms Itsines and her partner Tobi Pearce are the brains behind the Bikini Body Workout program and fitness app Sweat.

With 20 million followers they've amassed a combined fortune of $486 million, according to the Australian Financial Review's Young Rich List for 2018.

The couple set up their Bikini Body Training business in 2013 and a year later launched a 12-week workout and diet program, which later morphed into their hugely popular fitness app.

The 20-somethings have enjoyed one of the biggest rises on the list this year, leaping from 40th spot in 2017 list into fifth place this year.

Joining them in the top 10 are Collis and Cyan Ta'eed, the husband-and-wife co-founders of online graphic marketplace Envato whose fortune has doubled in the past year to $428 million.

Mrs Ta'eed and Ms Itsines are the only two women to appear in the top 10 of this year's list of Australia's wealthiest self-made businesspeople aged 40 and under.

Atlassian founders Mike Cannon-Brookes and Scott Farquhar came in on top for a record seventh year, with their fortunes more than doubling to $14.2 billion.

The software gurus' combined wealth is more than 14 times that of the next two on the list, Melbourne luxury property developer Tim Gurner and New York-based Ori Allen, whose real estate tech business Compass has made a big splash in the US.

Gurner, who is worth $631 million, created controversy last year when he warned millennials they would never be able to afford their first home if they don't give up spending $40 a day on smashed avocados and coffees while not working.

There are 21 newcomers on this year's list, including former Australian cricket captain Steve Smith and Formula 1 driver Daniel Ricciardo.

Most of those on the list have made their fortunes in the technology and finance sectors, as well as through sport.